1. Field of the Invention
The invention concerns a process and equipment for treating the surface of metallic strip material, especially for pickling rolled material, which is transported through a treatment channel and sprayed by jets with a pickling solution that contains acid. The jets at the entrance to the channel are directed in the direction of transport of the strip, and those at the exit of the channel are directed in the opposite direction to prevent the pickling solution from flowing off too quickly.
2. Description of the Related Art
In addition to a treatment process that involves laminar flow of the pickling solution, pickling with turbulent flow of the solution is known, in which the metal strip moves through a channel in a flat, horizontal position. The metal strip is supported from below on slide rings. At the channel entrance, jets of pickling solution are sprayed by nozzles onto the upper surface of the strip. This forms a film of pickling solution on the upper surface of the strip. At the channel exit, pickling solution is also sprayed in jets onto the upper surface of the strip, but in this case it is sprayed in the direction opposite the direction of transport of the strip, so that the film of pickling solution is maintained, and the pickling solution is kept from flowing out of the pickling bath at the exit.
Previously known treatment processes basically involve devices for altering and improving the flow conditions in the channel. The goal of these endeavors is to increase the exchange of pickling solution at the surface of the strip and thus to reduce the required pickling times, i.e., the residence times of a strip surface unit in the pickling solution.
DE-OS 29 11 701 describes a process and equipment for treating sheets of material in a treatment chamber. Successive turbulent streams of the treatment solution are directed at the two surfaces of the sheet of material inside the treatment chamber under pressure at an angle of much less than 90° and in the opposite direction from the direction of movement of the sheet, so that the sheet is treated and at the same time is guided in a more or less horizontal path through the treatment chamber through the bath of solution that is forming. However, the jets of pickling solution are directed only in the specified direction. Therefore, the formation of a film of pickling solution is not taken into consideration, and thus the consumption of pickling solution is very high.
The process specified at the beginning is described, for example, in DE 40 31 234 C2. In this process, the treatment liquid is fed at an acute angle against the material to be treated above and below the material, in opposite directions, and from both longitudinal sides.
EP 0,482,725 A1 describes a process in which optimum pickling results are obtained with minimum consumption of pickling solution by controlling the turbulence of the flow in the pickling solution as a function of the rate at which the strip to be pickled passes through. However, this is only a control process for some parameters of the pickling process.
In addition, double injection of pickling solution between the channel entrance and the channel exit is also known from EP 602,437 A1. In this case, the pickling solution is injected on both sides, above and below the plane of travel of the strip. However, other than the rows of injection nozzles at the channel entrance and exit, no means are provided for directing the pickling solution.
Finally, DE-OS 36 29 894 describes a process in which a treatment channel is located inside a tank, and, to support the oppositely directed rows of injection nozzles at the channel entrance and exit, rows of nozzles are also placed below the hot-rolled strips. However, these additional rows of nozzles merely increase the amount of pickling solution but do not have any effect on the flow.